This invention is an improvement over the system described and claimed in my U.S. Pat. No. 5,928,040, issued Jul. 22, 1999. This invention relates to the operation of a vessel having a propeller, and more particularly to a system for determining and displaying the real-time apparent slip and angle of attack for the vessel's propeller, as well as recording the same information for analysis at a later time.
Theoretical propeller advance in a non-yielding fluid is equal to the propeller's pitch multiplied by the number of rotations of the propeller. Apparent slip is the percentage of theoretical propeller advance lost in a yielding fluid, such as water or air. While apparent slip is not a direct measure of propeller efficiency, there is a strong correspondence between the two quantities. All other things being equal, as apparent slip is reduced, vessel speed increases.
Angle of attack is the difference between the theoretical and actual blade path for a rotating propeller blade. Angle of attack is necessary for a rotating propeller blade to generate the thrust also known as "lift") that moves the vessel. The angle of attack of a propeller blade causes a pressure differential between the opposite-facing surfaces of the propeller blade in the same manner that a wing or hydrofoil creates a pressure differential above and below the wing or hydrofoil as it moves through air or water. A propeller having no angle of attack will provide no thrust. The optimum range of angle of attack for a propeller blade is between about 3.degree. and 5.degree.. A propeller operating outside of this optimum range may cause excessive propeller slip or may cause the vessel's engine to operate outside the manufacturer's recommended range of engine speeds.
Traditional systems for monitoring motor vessel performance focus on the fuel efficiency of the motor vessel engine. None of these traditional systems provide an accurate measurement of apparent slip and angle of attack.
In propeller-driven vessels (e.g., fishing boats, water ski boats, remotley-controlled model airplanes and boats, and commercial and private airplanes), apparent slip and angle of attack are important factors in overall vessel performance. For some professional, personal, and recreational activities, the apparent slip and angle of attack of the vessel's propeller directly impact the success one might have in those activities.
For example, in sports fishing, most tournaments are structured such that all teams are allotted the same amount of time on a body of water. It is in a fishing team's interest to have a fishing boat equipped with a propeller that is operating with optimal apparent slip and angle of attack. The team that can move from location to location on the water the fastest, and therefore spend the greatest portion of its allotted time fishing, has the best odds of catching a greater number of large fish and winning the tournament.
Therefore it is desirable to provide a system that measures and records data relating to propeller apparent slip and angle of attack, and that allows comparison of apparent slip and angle of attack for different propellers and under different conditions.